Balancing barn life with anything is going to take some give and take. Sometimes you'll have to give up some barn time in favor of family obligations, or even doing something fun with your kids. Sometimes, you have to take some "mom time", though.
Maybe you should consider letting your green horse take some time off until the weather gets warmer and you can go after work. Work with your other horse on the barn days, and let the greenie just be a horse until you have time to spend. If you can start riding him at night soon then you can put him back into consistent work. Come summer time, you may find that the kids are more interested in riding and you can ride together. Sometimes kids need to suck it up and hang around with their parents during "boring" times, but it doesn't seem fair to subject them to it on a regular basis if they dislike it. Forcing barn trips on them may also be a good way for them to be off put of horses.
Also, how horsey is your horsey kid? If her interest in her pony involves riding once in awhile and that's it, then you need to reconsider keeping the pony. For the upkeep of the pony you could just pay for her to take lessons when she's interested. If it's a horse that you are actually interested in riding then it's great to keep her, but I wouldn't keep her around for the kids if they aren't going to do much with her and you don't have the time or inclination to spend with her. If she's a good, kids safe pony then you should be able to full or half lease her pretty easily. In fact, a half lease with you riding her a couple of times per week to keep her in check would probably be a good situation for both parties. She'd also still be there if your kids wanted to ride. Evaluate your needs and decide which horses YOU actually want to work with. Decide whether your kids are interested enough in the pony to keep her if you're not interested in working with her.